Grant County herald. [volume] (Lancaster, Wis.) 1850-1968, 1887-08-04
Forests and Rainfall.

The tangle Of decayed vegetation
which covers the ground beneath the
forest is of considerable thickness.
On the top it consists altogether OF
the decayed trunks, branches and
leaves, but it shades downward into
ordinary dark-colored soil, at depth
of few feet from the surface. This,
the decay zona of the forest, lies be-
tween the boughs of the air and the
branches of the roots. In it 90 on the
most important actions which take
place in our forests-actions which af-
feet the history of land and sea. We
shall therefore have to consider it in
somewhat painstaking way. The most
evident effect of this sheet of decay
ing wood and moss which feeds ON the
decay, is on the rainfall of the region
which it nantes. When, after sea
son of drought, a copious rain falls on
this spongy mass, the water is for
long time absorbed in the interstices,
and does not flow TO the rivers. Even
in times of heavy rain the water is
slowly yielded to the streams; after
dry period of many weeks this sponge
retains good share of water. A like
amount of water falling ON titled
fields or prairies slips quickly away to
the rivers and thence TO the sea. The
first result is that when the land is
destitute of forests it sheds water like
house roofs, breeding floods after every
considerable rain, while in the forests
the rain is only slowly yielded to the
streams.
A ri q
the spongy character of the forest bed
is that, by hindering the escape of the
rain-water to the rivers, it increases
the actual rainfall of the country. To
see the nature and Importance of this
action we must turn aside for mo-.
ment to consider the origin of the
rain which falls upon the land. The
original source of this water supply is
the sea, which sends into the lands q
tolerably regular supply annually of
moisture. When this falls as rain or
snow, either of the two things may
happen-the water may go away di-
rectly to the sea, or it may return to
the atmosphere as vapor, TO be again
precipitated as rain. The chance of
the re-evaporation is determined by
thespeed with which it flows to the
streams. From treeless region it
rapidly escapes; in an extensive region
OF virgin forest it may again and
again pass from earth to air, and from
air to earth.
The columns of vapOr, which in
times of summer rain may be seen
ascending from every great wood. af-
ford visible evidence of the effect of
the forests on rainfall. They also may
show the observer some of the most
beautiful phenomena of atmospheric
circulation. In Il summer rain shower
the air above the trees becomes much
cooler than it is in the reecsses below
their tents of foliage. The heated air
within the woods seeks to rise and es-
cape in great columns whenever there
is wide gap between the branches;
as soon as it attains the cooler level
above, the moisture is condensed, and
the air, before transparent, becomes
surcharged with steam. To replace
this ascending air broad current
drifts toward the emerging stream of
vapor, commonly from the highest
parts of the forest, where the air, ow-
ing to the elevation OF the ste, is cooler
than in the lower levels.
The repeated passage Of the moist
ure from earth tocloud and from cloud
to earth, greatly increases the amount
of force which the rain applies in its
falling drops to the earths surface;
but the rank vegetation protects the
surface from the erosion which it
would otherwise bring about Even
the forest clad hills.des of the Cum
berland mountains where the soil lies
on decliyities of great steepness, suf-
fer little wear as long rs their natural
protection is icft 10 them. But as
soon rs they are stripped of the gar
ment of wood which has been upon
the region ever since, in the far of
ages, they came from the depths of
the sea, they wear with great rapid
ity. The erosion is limited. rs they
are forest clad, to the stream beds, and
there is hindercd by the innumerable
obstacles of the fallen trees and en-
tangled driftwood. The brooks which
are strong enough to clear their beds
and cut into the earth and rock are
few in number; we may often, on the
flatter ground, find tracts of square
mile or SO in area in which there is not
a single stream that ever assails the
surface of the earth As soon, how
ever, rs the forest mat is removed, the
surface becomes scanned with chan
nels; they often, ON the dcforested sur
face, increase one hundred fold in
their length and morethan that meas
ure in their destructive power. Re-.
lieved of all restraint from fallen tim
Der, of the close Knit roots which inn
mesh the earth, they sweep precious
soil away toward the sea. In single
day titled liuid may lose from its
surface more soil than would be taken
from it in Il century of its forest state.
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